This invention relates to air conditioning and, in particular, to an air conditioning unit having improved air handling characteristics and reduced noise levels.
Improving the operating performance of packaged air conditioners, such as room window units, is an on-going effort in the air conditioning industry. The control of the return air flow through this type of compact unit poses special problems because of the restricted amount of space that is available within the unit. Typically centrifugal blowers are used to draw comfort air into the unit and through a heat exchanger for either heating or cooling the air in the flow stream. After passing through the heat exchanger, the conditioned air is drawn into the blower where it is turned 90 degrees before being discharged into a return duct. Typically the impeller used is a drum shaped assembly having a front shroud ring and a closed back wall that are connected by a series of axially disposed curved blades spaced about the drum periphery. The incoming air must turn from an axial direction to a radial direction to enter the impeller blades.
A bell mouth orifice is used at the inlet to the blower to gather the air drawn over the heat exchanger surfaces and conduct it into the impeller inlet. A narrow clearance gap is maintained between the moving impeller and the discharge end of the orifice. Unwanted air is drawn radially through the gap and across the front of the impeller, interfering with the inlet airflow. The velocity of the radially moving flow is relatively high and, as a consequence, a disturbance is created within the inlet region of the impeller. It has also been found that this disturbance in the incoming flow pattern increases the axial width of the stagnated air within the impeller itself which considerably reduces the amount of air that can be effectively passed through the impeller. In some cases the blower capacity may be reduced as much as fifty percent. As a consequence, the impeller is required to work harder in order to deliver the necessary system flow and the noise produced by the impeller is relatively high.